Bonding of paper using latex-dispersions of copolymers made of hydrophobic monomers/polymers of styrene/maleic anhydride type of low molecular mass

ABSTRACT

Such latex-dispersions used in paper bonding formulations make it possible to obtain acceptable COBB values, even with printing and writing papers or wrapping papers obtained from recycled or de-inked mechanical pulps.

[0001] The present invention relates to the surface treatment of printing and writing papers or wrapping papers.

[0002] It is known to use, for surface bonding of paper, printing agents consisting of latex dispersions made by polymerization or copolymerization of hydrophobic monomers in an aqueous solution of water-soluble or water-dispersible anionic polymers, in particular styrene/maleic anhydride copolymers, as taught by German patent DE 25 48393. These products were satisfactory, at least when the papers were made from fresh pulps. With mechanical pulps or pulps which are 100% recycled or simply partially recycled, it becomes very difficult, or even impossible, to obtain papers with satisfactory wet strength. This phenomenon, which can already be seen for “printing and writing” papers, becomes a major problem for wrapping papers.

[0003] It has just been found that bonding compositions based on latexes which are based on low-molecular-weight styrene/maleic anhydride copolymers provide an unexpected solution to the problem.

[0004] The invention is thus the application of latex-dispersions, such as those resulting from the polymerization of a mixture of hydrophobic monomers composed of styrene and of (meth)acrylic esters in emulsion in an aqueous solution of a water-soluble or water-dispersible amphiphilic copolymer consisting of a combination of hydrophobic monomers and hydrophilic monomers bearing carboxylic acid functions, in the presence of a radical initiator, in which the said amphiphilic copolymer has a molecular mass of between 500 and 5,000, to the bonding of printing and writing papers and wrapping papers, and more particularly to such papers obtained from recycled pulps. In the latex-dispersion, the copolymer with a molecular mass of between 500 and 5,000 is preferably a copolymer of one or more hydrophobic monomers taken from the group consisting of styrene or derivatives thereof, isobutylene or derivatives thereof and (meth)acrylic esters and of one or more hydrophilic monomers taken from the group consisting of (meth)acrylic acid and maleic anhydride, it being possible for the latter to be partially modified with an alcohol or an amine while at the same time remaining water-soluble or water-dispersible in aqueous medium, in particular a copolymer of styrene and of maleic anhydride in which the anhydride part may or may not be modified with an alcohol or an amine and in which the acid number is between 150 and 500. The polymerized hydrophobic monomers in emulsion in the aqueous solution of the amphiphilic copolymer are monomers of the group consisting of styrene and derivatives thereof, (meth)acrylic esters, including fluoro(meth)acrylic esters resulting from the esterification of (meth)acrylic acid with a perfluoro alcohol, or a mixture of these monomers.

[0005] The use of the latex-dispersions according to the invention may also be appreciated in the treatment of packaging cartons made from recycled pulps, for which a certain level of water-resistance is sought.

EXAMPLES Example 1

[0006] Preparation of a Latex According to the Invention.

[0007] 1,269 g of an oligomer with a molecular mass equal to 1,900, consisting of 74.3% by mass of styrene and 25.7% by mass of maleic anhydride, 6,825 g of demineralized water and 500 g of 28% aqueous ammonia are introduced in order into a 20 liter three-necked glass reactor fitted with a mechanical stirrer. The reaction mixture is heated to 60° C. and kept stirring until the oligomer has dissolved. The solution is brought to 85° C. and a mixture of 1,374 g of styrene and 1,587 g of butyl acrylate is then added under nitrogen with stirring, along with a solution of 52.9 g of (NH₄)₂S₂O₈ in 1,057 g of water, this being carried out continuously for two hours using pumps for metering out the oligomer solution prepared above, at 85° C. The reaction medium is maintained at 85° C. for a further 2 hours and is then cooled with gentle stirring.

[0008] A latex whose characteristics are as below is obtained:

[0009] Solids=23.5%

[0010] Brookfield viscosity at 23° C.=20 mpa.s

[0011] pH=8.85

[0012] Average particle diameter=55 nm

Example 2

[0013] This example shows the advantage of the bonding agents according to the invention for the surface treatment of printing and writing papers as regards their water-resistance.

[0014] The quality of the final bonding is evaluated by the COBB test which is well known to those skilled in the art, and is carried out according to NF standard EN 20535-ISO 535. The COBB test is performed here with a contact time of 60 seconds.

[0015] The treatment is carried out using a laboratory size press on two types of paper, one of them having a weight per unit area of 70 g/m², without internal bonding, and the other of 90 g/m², which may or may not have undergone internal bonding with alkylketene dimer (Aquapel® 315 from Hercules, referred to herein below as AKD). The two papers are manufactured from a fresh chemical pulp.

[0016] The test reports the results of the bonding obtained with aqueous compositions containing:

[0017] 5% by weight of AMYLIS® 100 P (Roquette) anionic starch,

[0018] 2.5%, 5% or 10%, by weight of active material, of latex-dispersion,

[0019] the composition being made up to 100% by adding the required remainder of deionized water for this purpose.

[0020] The latex-dispersion according to the invention is that which has been described in Example 1. The comparative product according to the prior art is the dispersion of Example 7 of U.S. Pat. No. DE 2,548,393.

[0021] The following were obtained on a paper which was not internally bonded: COBB 60 COBB 60 COBB 60 Product at 2.5% at 5% at 10% According to the >100    90 35 invention According to the >100 >100 55 prior art

[0022] The following were obtained on a paper which was internally bonded with AKD COBB 60 COBB 60 COBB 60 Product at 2.5% at 5% at 10% According to the 36 35 28 invention According to the 49 40 33 prior art

[0023] It is estimated that an acceptable printing and writing paper should have a COBB 60 of less than 30-40. On this basis, it is easy to see the undeniable advantage of the latex-dispersions of the invention over those of the prior art.

Example 3

[0024] In this example, the paper is manufactured with no internal bonding agent, either from a de-inked mechanical pulp or with a recycled pulp. The treatment was carried out on a pilot paper machine with three rates of introduction equivalent to a deposition of surface bonding agents—those of the above example—of 9, 12 and 15 kg/tonne of paper for the first support and of 3, 6 and 12 kg/t. for the second.

[0025] The following were obtained on a de-inked mechanical pulp COBB 60 COBB 60 COBB 60 Product at 9 kg/t. at 12 kg/t. at 15 kg/t. According to  81 46 28 the invention According to 123 98 78 the prior art

[0026] The following were obtained on a 100% recycled pulp COBB 60 COBB 60 COBB 60 Product at 3 kg/t. at 6 kg/t. at 12 kg/t. According to 140 120  25 the invention According to 145 120 100 the prior art

[0027] These results show that the bonding agent of the invention gives a sufficient bonding for deposition rates of 12 to 15 kg/t. whereas the comparative product does not make it possible to approach a satisfactory level of bonding at this rate of use. 

1. Application of latex-dispersions, such as those resulting from the polymerization of a mixture of hydrophobic monomers composed of styrene and of (meth)acrylic esters in emulsion in an aqueous solution of a water-soluble or water-dispersible amphiphilic copolymer consisting of a combination of hydrophobic monomers and hydrophilic monomers bearing carboxylic acid functions, in the presence of a radical initiator, in which the said amphiphilic copolymer has a molecular mass of between 500 and 5,000, to the bonding of papers.
 2. Application of latex-dispersions according to claim 1, characterized in that, in the latex-dispersions, the copolymer with a molecular mass of between 500 and 5,000 is a copolymer of one or more hydrophobic monomers taken from the group consisting of styrene or derivatives thereof, isobutylene or derivatives thereof and (meth)acrylic esters and of one or more hydrophilic monomers taken from the group consisting of (meth)acrylic acid and maleic anhydride, it being possible for the latter to be partially modified with an alcohol or an amine while at the same time remaining water-soluble or water-dispersible in aqueous medium.
 3. Application of latex-dispersions according to claim 1, characterized in that, in the latex-dispersions, the copolymer with a molecular mass of between 500 and 5,000 is a copolymer of styrene and of maleic anhydride in which the anhydride part may or may not be modified with an alcohol or an amine and in which the acid number is between 150 and
 500. 4. Application of latex-dispersions according to claim 1, characterized in that, in the latex-dispersions, the hydrophobic monomers are taken from the group consisting of styrene and derivatives thereof, (meth)acrylic esters, including fluoro(meth)acrylic esters resulting from the esterification of (meth)acrylic acid with a perfluoro alcohol, or a mixture of these monomers.
 5. Application according to any one of claims 1 to 4, in which the paper is a printing and writing paper.
 6. Application according to any one of claims 1 to 4, in which the paper is a wrapping paper.
 7. Application according to any one of claims 1 to 4, in which the paper is a wrapping paper made from a de-inked mechanical pulp or from a recycled pulp. 